Growing attention has been given to the potential of a pulmonary absorption route for non-invasive administration and systemic delivery of therapeutic agents (mainly peptides and proteins) because the lungs are capable of providing a large absorptive surface area (up to 100 m2) and have absorptive mucosal membranes that are very or extremely thin (e.g., have a thickness of about 0.1 μm-0.2 μm) and have good blood supply. A very thin alveolar-capillary and a bronchial-capillary barrier on a surface of the lungs allows for rapid uptake of human insulin particles into a subject's bloodstream, at a rate similar to that achieved with the rapid-acting human insulin analogue, which is an altered form of human insulin that is different from human insulin that occurs in nature, but still functions in the human body in a manner similar to human insulin, but with better performance in terms of glycemic control.
Insulin formulations may be administered by subcutaneous or intravenous injection. Inhaled insulin appears to be as effective as injected short-acting insulin. Pulmonary delivery technology was developed so that inhaled insulin can effectively reach the lung capillaries where it is absorbed.
Human lung airways contain bronchial tubes, which are impermeable to insulin, as well as alveoli. Inhaled insulin can be absorbed through the alveoli and enter into the circulation system. Inhaled asthma medications deposit before reaching the alveoli. Devices can deliver human insulin particles via slow and even breaths into the alveoli, and the human insulin can be released into the circulation system.
Inhaled human insulin may be used for pre-meal insulin delivery in people with type I and/or II diabetes. Its use may also facilitate the early introduction of insulin therapy to people who are averse to insulin injections due to reactions, such as inflammation, bruising, anxiety, and the like.